Process for the continuous manufacture of porous writing tips

ABSTRACT

A METHOD OF MAKING ELONGATED, ROD-LIKE OBJECTS ADAPTED FOR USE AS POINTS FOR WRITING INSTRUMENTS. STEPS INCLUDE POSITIONING A BUNDLE OF PARALLEL STRANDS OF SYNTHETIC FIBERS IN DESIRED RELATION BY DRAWING THE BUNDLE THROUGH A HEAT SETTING ZONE TO ESTABLISH DIMENSIONS AND CROSS-SECTION OF FINAL OBJECT AND ESTABLISH LONGITUDINALLY EXTENDING CHANNELS, AND SUBSEQUENTLY INCREASING THE STRENGTH OF THE OBJECTS BY IMMERSION IN A DILUTE RESIN SOLUTION AND HEATING TO EVAPORATE SOLVENT AND TO CURE THE RESIN.   D R A W I N G

. Jan. 1971 L, GQQDENQW ET AL 3,558,392

PROCESS FOR THE CONTINUOUS MANUFACIURE OF POROUS WRITING LIPS 4 Filed June 27, 1966 I VEN roles. 105 L. Goons/vow (l /WES OSzmuww .Dmwaz. ISEEEGELY United States Patent 3 558 392 PROCESS FOR THE COfiITINUOUS MANUFAC- TURE 0F POROUS WRITING 'nrs Elden Lucerne Goodenow, Los Angeles, James OSullivan,

Culver City, and Daniel W. Seregely, Los Angeles, Calif., assignors to The Gillette Company, Boston, Mass., a corporation of Delaware Filed June 27, 1966, Ser. No. 560,405 Int. Cl. B431: 1/12; D04h 3/14 US. Cl. 156-180 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process of continuously manufacturing porous Writing tips whereby uniform and reproducible products can be obtained.

The development of writing instruments which employ porous tips (instead of metallic nibs) is based upon the earlier devices for applying water to gummed surfaces, shoe blacking, etc. and utilized tips made of felt, sponge, etc. These prior devices employed rather soft, easily doformable applicating ends which produced very wide, rather brush-like strokes and therefore could not be used for normal writing of letters, where a relatively thin, uniform line is desired.

Many problems have been encountered in attempting to produce uniform, reproducible tips capable of depositing a written line of suitable delicacy; it was found that the entire structure of the tip had to conform to many standards and limitations such as density, strength, flexibility, ability to feed ink to the tip in a uniform manner so as to permit rapid writing, and, at the same time, not accumulate gobs of ink during periods of non-use, etc. Uniformly distributed channels and pores must be provided for the ink and such channels should be within a suitable range of transverse average width size and area. Furthermore, an acceptable writing tip must write smoothly, with very little, if any, resistance and without squeakmg.

The present invention is directed to an economical, continuous manufacturing process whereby under controlled conditions, the structure, density, flexibility and other requirements can be controlled so that' uniform writing tips, of uniform characteristics, may be manufactured in a reproducible manner. The materials, conditions and sequence of steps hereinafter described permit the manufacture of writing tips in a reproducible manner so that the entire output can either consist of relatively hard, non-flexible fine writing tips or, when it is desired to produce a softer writing tip capable of producing a line of greater width and shading, the operator can be assured that all of the tips will now conform to the predetermined standards of strength, density, flexibility, porosity, feeding characteristics, etc., which characterize such tips. It will be readily recognized that the economical manufacture of tremendous numbers of writing tips precludes individual testing of each tip, and therefore the process must be capable of control so as to insure predetermined uniformity.

Generally stated, the present invention utilizes yarns selected from the family of thermoplastic fibers (since p CC natural fibers are not satisfactory), the arrangement of such fibers in substantially parallel longitudinal relation and suitably spaced from each other so as to form a predetermined array (generally cylindrical), heat treating the cylindrical bundle to form a preliminary structure of desired porosity and size, then fixing the fibers in such desired position with respect to each other and with the longitudinally extending porosities or channels of a desired size and distribution, and curing the fixed or resin treated rods so as to produce a continuously moving rod which now can be cut, have its ends shaped and otherwise treated for use as a writing tip. The materials and conditions which permit continuous, rapid manufacture of reproducible, substantially uniform writing tips will be described in detail hereafter.

An object of the present invention is to disclose and provide a methodfor continuously manufacturing writing tips of substantially uniform writing characteristics and other properties which affect the efliciency and the effectiveness of the writing tip.

A still further object of the invention is to disclose and provide materials, conditions, treating agents and process steps which insure the attainment of the objects of this invention.

These and various other objects and advantages of the present invention will become apparent from the following description; for purposes of illustration and in order to facilitate understanding, reference will be had to the appended drawings wherein:

FIG. 1 is a diagrammatic representation of the various stages and operations involved in the continuous process;

FIGS. 2 and 3 are enlarged somewhat diagrammatic representations of partial cross-sections taken through an exemplary writing tip in the course of its manufacture.

As previously indicated, the body material of the porous writing tips is composed of any one or more synthetic, preferably thermoplastic fibers such as polyvinyl chloride, polyethylene, polyethylene terephthalate, polypropylene, polyacrylonitrile and copolymers with vinyl acetate, cellulose acetate and various polyamides such as nylon 6 and nylon 66. As shown in FIG. 1, the selected yarn supply 1, in the form of a plurality of spools, bobbins or reels 2, 2, etc., is provided. The spools are preferably provided with individually adjustable friction drags so as to control the tension in the strands which are drawn from the reels. Each yarn strand is passed through a perforation in a gathering or arranging plate generally indicated at 4, the perforations or openings being smooth- Walled and in circular array. The individual openings are closely spaced, may be about Ms" in diameter and provided with conical or flaring inlets so as to facilitate the feeding of the strands therethrough. The number of individual strands employed will vary with the size of the Writing tip desired; from 17 to as high as 60 strands of yarn may be used depending upon the total denier of the yarn employed and the final diameter or other form of the writing tip being manufactured. For example, in the manufacture of a writing tip which will finally have an outside diameter of about 0.1", a crimped yarn having an uncrimped denier of 1050, composed of 70 continuous filaments, can be successfully used. The total denier of the entire assembly may vary from between 25,000 and 40,000, a preferred range (for the exemplary sized tip) being between about 28,000 and 32,000. The filament denier may range from as small as 1.5 d.p.f. to 18 d.p.f. or even larger.

The perforated metal plate gathers and properly arranges and positions the individual strands of yarn in accordance with a predetermined pattern. The procedure insures the desired placement of the individual strands of yarn in the completed writing tip with longitudinally extending channels dispersed between the strands, It is to be understood that all of the strands are constantly under tension (on the order of 2 to 6 grams per strand at the feed end) and are being pulled from the supply reels in zone 1 by means at the far end of the production line hereinafter described. The gathered strands are then passed through a drying zone generally indicated at 6; this drying tube may comprise a tube 7 (having a diameter from 2 to 8 times the diameter of the ultimate product). The tube may be lined with a polytetrafluoro composition capable of presenting a surface of a low coefficient of friction. The tube may be enclosed by an electrically heated housing 8. The temperatures in this zone should not be sufficiently high to produce any softening of the filaments or strands but only sufiicient to dry the strands; when nylon is used temperatures on the order of 130 C.175 C. are adequate when the strands are drawn at from about /2 to 2 feet a minute, the length of the treating zone being a factor. Purging of water vapor and other volatile material from the fibrous strands is facilitated by passing nitrogen or other inert gas through the tube in a direction countercurrent to the movement of the fibers.

The now dried bundle of strands is passed through another tunnel which has an internal contour or diameter of the required size and establishes the external contour or diameter of the finished writing tip or applicator. This tunnel 10 provides a heat-setting zone indicated generally as 9, has a flaring inlet and is lined with heat resistant material of low coeflicient of friction; it is surrounded by a heating chamber 11. The temperature in this heatsetting zone is very accurately controlled so that the bundle of yarn, while moving under tension, in longitudinally extending relation and in the relative cross-sectional distribution established in the positioning zone 4, is here compressed and subjected to a temperature below the melting point of the yarn but sufficient to cause softening and adherence of the adjoining strands (or crimped portions thereof) to each other, the time, temperature and tension being insufiicient to completely destroy the crimped form of all of the crimped filaments in the bundle. When employing nylon 6 yarn (which has a melting point of about 220 C.) a temperature 3 to 6 lower (say 216 C.) is maintained, it being understood that the temperature may have to be varied in accordance with the speed of travel of the yarn through the heat-set zone 9 and the characteristics of the yarn being employed. The heat setting operation appears to produce a random discontinuous and minute incipient fusion which bonds the strands without forming nodules or droplets of solid matter. After the heat setting operation, very little residual crimp is visible and the average fiber direction in the heatset bundle or rod does not appear to depart more than about from the rod axis. It is highly desirable that the porosity of the tip, as it is discharged from the heat setting zone, be maintained in a high range, for example, at the stage indicated by the section line II-II, between 25% and 95% of total volume of the bundle should be pores and channels.

The heat-set bundle of yarn now passes through a cooling zone 12 and an enlarged somewhat diagrammatic transverse section taken through the bundle at the plane II-II is illustrated in FIG. 2. At this stage of the continuous operation, the bundle is coherent and the individual strands are in the positions desired with longitudinally extending channels or pores of a desired average dimension and distribution. It will be noted from an examination of FIG. 2 that a certain proportion of the individual strands (particularly formerl crimped filament portions thereof) have been caused to sinter together; they are heat-bound to each other, as for example, the fibers 3, 3', and 3", but it will be noticed that longitudinally extending channels or pores, such as 13 and 13', exist and such channels are rather uniformly distributed throughout the cross-section of the partially completed writing tip.

The preset bundle of yarn now passes through an impregnation zone '14. In the diagrammatic representation, this impregnation zone is shown to include a tube 15 with short, very gently upwardly inclined end portions, the tube being constantly supplied with a dilute solution of resin in a volatile solvent from a reservoir 16 through a valved supply line leading to the central section of the tunnel. When a plurality of production lines are used, a tray-like arrangement takes the place of tube 15. The preset yarn bundle barely deviates by more than its diameter from a rectilinear path in its travel through 14. The entire tunnel may be enclosed by a temperature control bath 17. The exit end of tube 15 includes a rubber orifice which wipes excess resin solution from the treated bundle or rod. Although the density of the packing between individual strands of yarn and the arrangement of the yarn is well controlled by prior steps (and these factors influence the amount of resin solution that will be absorbed and the distribution of the resin among the fibers after the volatile solvent in which the resin is dissolved has evaporated), the impregnating step must be carried out at a temperature below the boiling point of the solvent and below the curing temperature of the resin. The concentration of the resin in the volatile solvent is also of considerable importance in insuring the proper distribution of the resin so that the resin does not accumulate in large clusters or droplets and does not block the passageways or channels in the writing tip; a large number of minute surface bonds between fibers produces the ideal combination of high strength and high porosity. Crimps in the fibers assist in producing a multiplicity of fiber-to-fiber contacts in which the resin is held. The crimps also provide frequent interruptions of excessively large contacts, insure that they remain unfilled with resin and thereby facilitate the retention of channels or passages for ink flow in the finished writing tip.

It has been found that the resin content of the impregnating solution can be in the range of 15% to 45% by weight (20% to 30% is preferred); higher concentrations within the range produce a hard tip whereas lower concentrations facilitate the production of a softer tip. A great variety of resins may be employed and those skilled in the art will appreciate that different catalysts, hardeners or curing additives may be employed if setting of the resin requires their presence. Addition polymers such as the epoxies, isocyanates, polyesters, vinyl compounds, acrylics, alkyd resins, silicones and acetals may be employed. For example, Epon 828 (a monomer manufactured by the Shell Chemical Co.) may be used and an aliphatic polyamine can be used as the hardening or curing agent; Epon 1001, which is a polymer, can also be employed using an acid anhydride as the catalyst. Tolylene diisocyanate and polymethylene, polyphenyl isocyanate polymer are other examples and polyamines or polyethers and glycols are representative of suitable hardeners. Acrylic resins manufactured by Rohm & Haas and Carbide & Chemical Corp., as well as various silicones such as SR-98, SR-17 and SR- may be used, subsequent heating being sufiicient to properly cure these resins. Polybutadiene-styrene copolymers and a di-vinyl benzene monomer are representative of satisfactory vinyl resins, whereas polyvinyl 'butyral polymer and polyvinyl formal are exemplary of acetals.

Various condensation polymers such as phenolics, resins of the melamine-urea-formaldehyde type, aldehydes such as the furane plastics, furfuraldehyde resins and monomers, acrylics such as Du Ponts Lucite polymers and epoxy resins, polyesters, polyvinyl acetates, Versalon 1175 (a polyamide polymer sold by General Mills) and similar thermoplastic systems can be used. It is to be understood that a catalyst, hardener or curing agent need not be present in all instances, since some of these thermoplastic systems dry and harden by the release of solvents (such as the acrylics, polyvinyl acetate and polyesters) and others set upon exposure to heat (as in the case of General Electrics silicone polymers, SR series, acrylic polymers and isocyanate polymers). The solvents to be employed should be relatively volatile and preferably capable of being removed at temperatures not greatly exceeding 125 C. and at all events below the melting point of the fibers. Solvents compatible with the resin used can be selected from ethers, esters, alcohols, aromatics, chlorinated solvents, ketones or glycol ethers, and may have boiling points as high as 175 C. or as low as 35 C. (diethyl ether).

Examples of resins and catalysts, hardeners or curing agents include:

Epon 828 (monomer, Shell Chemical Co.), plus 11.5%

triethylene tetramine.

Unox Epoxide 221 (Carbide & Chemical Corp.), plus 35% phthalic anhydride.

Eponol 55 L-32 (polymer, Shell Chemical Co.), plus '5.10*% isocyanate.

Tolylene diisocyanate, plus 35-50% meta phenylene diamine.

AR2076 (G.E. polyester), plus 1.0% benzoyl peroxide.

Di-vinyl benzene monomer, plus 1.0% benzoyl peroxide.

XAC 9 alkyd resin (Sherwin Williams), plus 0.l1.0%

cobalt naphthenate.

Aerotex M-3 melamine urea formaldehyde polymer (American Cyanamid), plus 5l0% MgCl Furfuraldehyde monomer, plus 15% NH Cl Polyvinyl acetate, dry to release solvent.

SR-98 silicone polymer (G.E.), (heat).

Butvar B-40 (polyvinyl butyral), plus 50% epoxy to cause cross-linkage.

After the lightly sintered bundle of fibers has been impregnated in zone 14, it is then drawn through the drying or solvent removal zone indicated at 18 and then through a heat curing zone generally indicated at 24-, although, in some instances, the drying and heat curing steps may be combined in one unit or zone. In the illustrated arrangement, the drying zone may simply consist of an elongated chamber 19 which may be heated in the event the solvent employed requires some heat to facilitate its removal. The solvent vapors may pass into a condenser, generally indicated at 20, for recovery. In some instances, the solvent removal step may be conducted in the open.

The next step is a curing of the preformed, continuously moving rod. As shown in the drawing, curing may take place in an elongated chamber 25 through which hot air is circulated by means of a motor driven fan 26, the air moving over suitable electric heating units generally indicated at 27, 27', etc Radiant heat may be employed directly within the primary drying chamber through which the preformed object is continuously drawn. As previously indicated, solvent removal and curing may take place concurrently in the same unit, or, in successive sections of a unit. Again, the temperature to which the preformed object is heated will depend upon the resin composition employed. For example, Epon 828-triethylene' tetramine can be cured at 180-190 C. for minutes.

The continuously moving, column is then cooled in a zone indicated at 28 and by section line III-.-III. The cooled object then passes through a series of rollers indicated at 30, these rollers constituting the tensioning and advancing means for the entire production line. The rollers are preferably contoured to fit around the object being formed, and are yieldingly pressed against the object and driven by suitable speed control mechanisms so that the strands being fed from the supply zone 1 are drawn at a predetermined speed and a suitable tension is applied to all of the strands throughout the production line. The tension on a continuously moving heat treated resin-bonded rod made of 23 strands is on the order of 3 to 5 lbs.; the tension on each of the strands being drawn off the supply reels is on the order of 3 to 4 grams. The

cooled cylinder, rod or other continuous formed object is then sent to zone 32 where mechanism cuts and preferably simultaneously forms the ends of the cut-off sections so as to produce completed writing tips of a desired length and contour at the shaped end or ends. These writing elements or tips can then be collected in baskets and suitably treated or sent to storage, sent to production for fitting into complete writing instruments, such as pens, etc.

In many instances it has been found desirable to treat the writing tips discharged from the cutting and forming zone 32. For example, it has been found desirable to treat the writing tips with a wetting agent so as to facilitate the wetting of the tips and the movement of ink through the minute channels or passageways in the tip. Any anionic or non-ionic wetting agent, such as for example, sodium dodecyl benzene sulfonate may be effectively used on the writing elements. In order to facilitate the application of such wetting agent to the interior surfaces of a finely porous writing tip, vacuum impregnation may be used, foraminous baskets filled with precut writing tips being immersed in a solution of wetting agent and subjected to subatmospheric pressure which facilitates removal of air and entry of the solution. In the treatment of writing tips made from nylon yarn and epoxy resin, immersion of the preformed tips into a 1% aqueous solution of sodium dodecyl benzene sulfonate has been found very effective particularly if combined with subatmospheric pressure treatment.

It is desirable to assemble such wetting agent treated tips with pen bodies and reservoirs before the tips have completely dried in order to establish good ink flow. Another procedure is to assemble the tip into a pen body, contact the dry tip with an ink reservoir and then apply a few drops of methyl or ethyl alcohol to the tip to facilitate ink feeding to the tip.

FIG. 3 is a partial section of a substantially completed resin-bonded writing tip, the section being taken along plane IIIIII in FIG. 1. By comparing FIG. 3 with FIG- 2, it will be noted that substantially the same arrangement and distribution of channels or passageways for the ink exists in FIG. 3 that existed in FIG. 2. It will be noted that the strands are now in bonded clusters of various cross-sectional form. The size or average transverse dimension of the channels has been but slightly decreased (since a minute coating of resin now bonds the various strands and particularly the crimped portions thereof) more firmly than the initial heat-set or sintering which took place in zone 9.

The main channels preferably have average or mean transverse dimensions of from 1 x 1 mils to 3 x 6 mils; channels of 1.5 to 3 mils in one transverse direction and between 3 and 6 in another direction are representative of most desirable channel sizes, and should predominate since 1 x 1 mil channels are relatively ineffective; some channels may measure 10 mils in one direction. The total number of channels and pores is lower in FIG. 3 than in FIG. 2, and there has been a reduction in the number. of minute spaces between the fibers. The total number of channels (in a preformed rod 0.1" in diameter) may vary within wide limits, depending upon the number of strands employed and denierof the filaments, but for writing tip products the number may be between about 200 and 600, the larger number occurring when filament of say 6 d.p.f. is used and the smaller number when say 15 d.p.f. is employed. The pore volume of the tips may be between about 15% and 70%.

One of the important characteristics of the products produced in accordance with this invention is that the individual channels are not longitudinally continuous from one end to another of a finished rod and rarely have an uninterrupted length of even /2". It is to be remembered that preferably the yarn is crimped and the crimped filaments often contact and become bonded, thereby tending to block the continuity of a discrete channel but each channel feeds into another short longitudinal channel. This characteristic structure of the product results in added strength and stiffness to the product and provides a multiplicity of interconnected small feeding reservoirs for ink whereby (when the product is used as a writing tip) movement of ink along the finished rod or tip is facilitated, ink is always available for writing purposes, but will not flow at an excessive rate nor flow or gob when subjected to shock. The writing tip will not dry out and be ineffective when a writing instrument has been left uncovered and exposed to air for a day or two; no difficulty is experienced in starting writing at any angle of the tip or writing instrument to the paper.

Cylindrical writing tip stock made by our method (from strands of Nylon 6) will show increase in stiifness (and ability to produce fine-writing points) as the concentration of bonding resin is increased, lower resin concentrations producing softer, broader-writing tips. Both types of tips appear to require the presence of channels having cross-sectional areas of the sizes noted above, such channels being readily observable at a magnification of say 45. From about 25% to about 40% of the total crosssectional area of writing tips may be constituted of these channels, the rest of the porosity being attributable to finer capillaries.

As previously indicated, the denier of filaments employed exerts an effect upon the number and size of the channels formed. The elfect is illustrated in the following table wherein A represents a cylindrical writing tip product made in accordance with this invention from 29 strands 840/136 Nylon 6 having a filament denier of 6 d.p.f., the binder being 31% of Epon 828, and B is a similar product made from 23 strand 1050/70 of d.p.f. filament using 28% Epon 828: each 0.1" in diameter.

Number Average Porosity, of main size, percent channels sq. in.

Product:

A 39 550 5. 54X10- B 33 250 10. 55X10" Density and porosity of the products obtained may be calculated from the densities of the synthetic fiber and resin employed. The effect of the resin treatment is illustrated by the following example, wherein Nylon 6 (having a density of 1.14 grams/ cc.) was used in the yarn and epoxy resin for the bonding step in the making of relatively rigid writing tips:

Density Porosity Head set only 0.61 gr./cc. 38%46 After resin impregnation and curing 0.75 gr./cc. 32%-40% Percent resin Deflection under 10 in samples: gram load, inches 22 .0l9.021 31 .019.020 40 .015.016

It may be noted at this point that some resins produce surfaces which are more readily wetted by ink than others and for this reason the impregnation step described hereinabove is not illustrated in FIG. 1, but has been mentioned since it provides a means of insuring greater uniformity and reproducibility of writing tips, and can be readily determined by testing with the particular ink composition being used.

It is to be understood that not all of the strands of yarn used in making the porous objects need be of the same denier nor of the same synthetic fiber, since advantage can be taken of different physical characteristics of different fibers. Also, when writing tips are being manufactured, the presence of a virtually non-porous outer skin is often advantageous since such tips are usually ground to a point and only the central or inner portion of the tip need be provided with a multiplicity of longitudinally extending, spaced channels or passageways for ink. The prepositioning in zones 4 and 6 is important in insuring the production of channels of desired size and number located in a desired uniform or homogenous manner.

It may be noted that in some instances it may be desirable to subject the heat-set bundle to two successive impregnations, one with a resinous component and then with a reactant, but economic considerations favor the use of a single resin solution impregnation followed by the use of heat.

By the use of the conditions and sequence of steps and materials herein disclosed, continuous rods of various cross-sectional shape can be manufactured in a controlled, continuous manner with assurance that physical characteristics such as structure, density, flexibility, size of channels, location of channels and strength can be produced with assurance.

All changes and modifications coming 'within the scope of the appended claims are embraced thereby.

We claim: 1. In a continuous method of making absorbent writing elements having a virtually uniform pore volume and pores having cross-sectional areas within controlled limits, the steps of:

continuously drawing strands of synthetic yarn including crimped filaments from a plurality of supply reels, each strand at virtually equal and uniform tension, through a yarn positioning zone to form an uncompressed cylindrical bundle; reducing the cross-sectional area of said bundle and drawing it through a heat-setting zone while maintaining said strands in longitudinally extending relation and in the relative cross-sectional distribution established in the positioning zone; subjecting the bundle while under tension in the heat setting zone to a temperature in the region of approximately the temperature of the melting point of the yarn for a time suflicient to cause softening and adherence of the adjoining strands to each other, whereby said bundle assumes a coherent cylindrical form of ultimate size having a pore volume on the order of between about 25 and of total volume;

then cooling said coherent bundle and drawing the cooled bundle through a dilute solution of a curable resin in a vaporizable solvent to impregnate the bundle at a temperature below the boiling point of the solvent and below the curing temperature of the resin;

passing the impregnated bundle through a solvent removal zone at a temperature below the melting point of the synthetic yarn to vaporize the solvent and leave a minute film of resin on at least some of the yarn surfaces;

and then drawing said bundle through a resin curing zone to cure the resin and form a relatively strong, formed porous bundle having a pore volume of between about 15% and 70%, composed in large part of longitudinally extending channels having transverse dimensions of between 1 mil and 10 mils.

2. In a method as stated in claim 1 wherein the dilute impregnating solution comprises a volatile solvent and a curable resin from the group consisting of monomers, addition polymers, condensation polymers and thermoplastic systems.

'3. In a method as stated in claim '2 wherein the volatile solvent is from the group consisting of ethers, esters, alcohols, aromatics, chlorinated compounds, ketones and glycol ethers, and has a boiling point not exceeding the melting point of the yarn.

4. In a method as stated in claim 2, the step of controlling the resin content of said resin solution to between about and 45% by weight and in controlling the time of contact between the coherent bundle and said solution.

5. In a method as stated in claim 4, the further step of cutting and trimming the formed bundle into writing elements and subjecting the writing elements to the action of an anionic or non-ionic wetting agent in solution.

6; In the controlled continuous manufacture of coherent elongated objects composed of synthetic fibers arranged in virtually parallel longitudinal relation and having longitudinally extending channels, such objects being adapted for use as Writing elements, the steps of: continuously passing a bundle of synthetic yarn strands under tension and in predetermined array in virtually parallel relationship through a heating zone to lightly sinter together some of said strands and produce a coherent object of a configuration established in said heating zone and simultaneously forming longitudinally extending channels between some of said sintered together strands;

continuously advancing the lightly sintered array to an impregnation zone and into contact with a solution of a hardenable resin in a volatile solvent, said solution being maintained below the boiling point of the solvent, while continuing to maintain said yarn under tension;

conducting said impregnation for a time and at a resin concentration insufficient to materially reduce 10 the longitudinally extending channels in the sintered array;

continuously drying and baking the impregnated sintered array while maintaining it under tension to harden the resin and bond adjacent yarns to each other to form strong objects of greater bulk density than the sintered array containing uniformly distributed, longitudinally extending channels within a desired range of average transverse dimension, said channels constituting 15 to of the total volume of the formed object.

7. A method as stated in claim 6 wherein the yarn strands are composed of a polyamide, the bundle is subjected to a temperature below the melting point of nylon in the said heating zone and said strands are held in an array designed to establish the distribution and size of the main longitudinally extending channels through the object.

References Cited UNITED STATES PATENTS 2,688,380 9/1954 MacHenry 156180UX 2,751,320 6/1956 Jacobs et al. 156180 2,757,111 7/ 1956 Henderson 156180 3,106,501 10/1963 Cobb, Jr., et al 156-180 3,111,702 11/1963 Berger 401199 3,189,506 6/1965 Cobb, Jr., et al l56296 3,400,998 9/1968 Daugherty et al. 401198 WILLIAM J. VAN BALEN, Primary Examiner R. O. LINKER, IR., Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3 ,558 ,392 January 26 1971 Dated Patent No.

Elden Lucerne Goodenow et a1 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the drawing line 2 "PROCESS FOR T1 CONTINUOUS MANUFACTURE OF POROUS WRITING LIPS" should read PROCESS FOR THE CONTINUOUS MANUFACTURE OF POROUS WRITING TIPS Column 7 line 49 "Head" should read Heat Signed and sealed this 20th day of July 1971 (SEAL) Attest:

WILLIAM E. SCHUYLER, JR

EDWARD M. FLETCHER,JR. Attesting Officer Commissioner of Patents 

